1. Field of the Invention
The present invention relates to a recording and/or reproducing apparatus in which while relatively two-dimensionally scanning a probe electrode to a recording medium, information is recorded onto the recording medium and the recorded information is reproduced by using a signal which is caused by a physical interaction between the recording medium and the probe electrode.
2. Related Background Art
In recent years, there has been a tendency to increase the recording capacity of a recording apparatus, to decrease the size of the recording unit and to increase the recording density. For example, in a digital audio disc recorded on using an optical recording, the size of recording unit is set to at most about 1 .mu.m.sup.2.
On the other hand, in recent years, a scanning tunneling microscope (hereinafter, simply abbreviated to STM) which can directly observe the shape of a surface of a substance and the electronic structure of a portion near the surface has been developed and an application in a wide range is expected because the STM has the following advantages.
1. A real space image can be measured at a high resolution irrespective of a difference between a monocrystal and an amorphous. PA1 2. An image can be observed at a low electric power consumption without damaging a recording medium with a current. PA1 3. The STM can operate not only in a superhigh vacuum but also in the atmosphere and in solution. PA1 4. The STM can be used for various kinds of materials.
The STM uses the phenomenon of a tunnel current flowing between a probe electrode (metal probe) and a conductive material when a voltage is applied therebetween and the probe electrode is made approach the material up to a distance of about 1 nm. The tunnel current is very sensitive to a change in distance between the probe electrode and the conductive material. Therefore, surface information of a real space can be obtained by scanning the probe in the in-plane direction while keeping the tunnel current or the average distance between them constant. In this instance, the resolution in the in-plane direction is equal to 10 nm or less.
By applying the principle of the STM and by using a thin film layer or the like of a material having a memory effect for the switching characteristics of the voltage to current, for example, a .pi. electron system organic compound or chalcogen compound class as a recording medium, information can be recorded on a recording unit basis of 0.01 .mu.m.sup.2 or less.
On the other hand, by using a method of changing the surface shape state of the medium by using an electromagnetic wave such as electron beam, light, or the like, although the recording unit increases because of a limitation of the convergence degree of the beam, information can be recorded and reproduced at a recording density that is almost equal to that in the present optical recording.
In the above conventional recording and reproducing apparatus using the principle of the STM mentioned above, however, in case of recording and reproducing information at a high density over the surface (recording surface) of the recording medium having a predetermined area, the S/N ratio, the error rate, or the like of the signal upon reproduction deteriorates due to concave and convex portions which are not concerned with the recording information existing on the recording surface. Such deterioration is a significant obstacle to developing a high density recording capacity.